1. Field of the Invention
This invention generally relates to display terminals which are connected to digital data processors for generating and reading stored alphanumeric text and, more specifically, it relates to mechanical Braille display terminals which are used to generate the stored text and to display the stored text in Braille.
2. Description of the Prior Art
People with serious visual impairments cannot use a computer terminal equipped with only a standard video display. For such people the computer is essentially inaccessible unless they have special equipment which converts the video display to Braille characters which can be read by touch. Two categories of such Braille interface equipment are available. There are Braille printers which will print onto paper the text which normally appears on a screen. They are similar to conventional printers except that they produce embossed Braille characters instead of inked characters. There are also devices known as mechanical Braille displays. They are located in a reading terminal which stands beside or is spatially isolated from the standard keyboard. The mechanical display includes a string or window of Braille display cells which display in raised Braille format a segment of the text which may also appear on a video screen or which may be stored in a hardcopy buffer memory. Each Braille cell is an electromechanical device including an array of pins movably mounted in a block so that the pins ends can be raised above or withdrawn beneath the surface of the block to create the desired Braille character. The user reads the text by electronically moving the window of Braille cells about the video screen or about the hardcopy buffer where the text is stored.
Although both systems help visually impaired people to use computers, each has significant limitations. The limitations of the Braille printers are particularly obvious. Like conventional printers, they are good for printing files but they are impractical for verifying input as it is being generated or for editing existing text. Each view of the text after additions or corrections are made to it requires another printing of the entire contents of the text file. Thus, relying on a Braille printer as a substitute for the video screen makes the computer exceedingly awkward and cumbersome to use.
Mechanical Braille display terminals on the other hand, are more suitable substitutes for the video screen; yet they too impede user efficiency in ways which are not quite so obvious and have largely gone unrecognized. To read what has been typed into the computer, the user shifts one hand away from the keyboard and over to the mechanical Braille display terminal where the text can then be read. Since the user cannot type and read at the same location, using the computer involves many wasted back and forth movements between the reading and the typing terminals. In terms of efficiency, this is analagous to requiring a sighted user to remove his hands from the keyboard before he can view the video display. Restricting the sighted user in such a manner would seriously diminish his efficiency and productivity. Similarly, requiring the visually impaired person to rely on a separate reading terminal significantly limits his efficiency and productivity. Thus, the separate Braille reading terminal imposes a mechanical barrier preventing the visually impaired person from approaching the efficiency and productivity of sighted users.
The significance of the mechanical barrier has gone unrecognized because the limitations on efficiency have been seen as inherent to the visual impairment. The prevailing understanding about how people read Braille taught that a multicell display and thus a separate Braille reading location was necessary. According to this understanding, the visually impaired reader does not read text one character at a time. Rather he reads much like a sighted reader does, by assimilating segments of text. In this manner, the words are perceived not by assembling the individual letters of which they are comprised but instead by seeing the word or phrase as a whole. Thus, when a person reads Braille, he does not identify each letter before moving on to the next one; instead he scans a segment of text with his fingers in an effort to recognize words and phrases. Missed words are reviewed by moving back on the line and rescanning it with the fingers. In this process, the index finger is the primary reading finger. Nevertheless, people have also thought that the other fingers play a role by providing useful preview information of characters before the index finger contacts them. Because the Braille reading process involves "looking" at segments of the line and may involve more than a single reading finger, it has been believed that an effective interface with a computer must therefore use a multicell display which simultaneously displays phrases or segments of the text being read. If a multicell display must be used, then the separate reading location is unavoidable and the consequent limitations on user efficiency naturally follow.